try to fix bundle failure on Win32

We have always gotten this error:

    Error rename on 'C:/.../share/theme/default/site/footer.html2068289669120' -> 'C:/.../share/theme/default/site/footer.html'':
    Permission denied at t/command.t line 359.

My current guess is that it's because the file already exists when we
try to rename something on top of it, so let's remove it first.